Internal combustion engines of small size are often equipped with a carburetor since this is a simple and inexpensive fuel supply unit. However, the functioning of the carburetor can be disturbed by the engine vibrations, especially if these vibrations are comparatively substantial. This is often the case with smaller one-cylinder engines. Furthermore, in a portable working tool, such as a chain saw, the power unit is spring-suspended in the tool unit, i.e. a so called anti-vibration suspension. It means that the vibrations will decrease in the tool while they as a rule will increase in the actual spring-suspended power unit. It is often desirable to create an anti-vibration suspension also for the carburetor itself, however, this is often complicated by the fact that the carburetor is situated close to the engine's cylinder. In such an anti-vibration carburetor suspension arrangement a flexible rubber bellow is being used as a connection between the carburetor and the cylinder. Air and fuel from the carburetor flow trough the bellow into the cylinder. As a rule pressure pulses from the engine's crankcase are used for pumping fuel into the carburetor. This implies a duct to be drawn from the engine's crankcase over to the carburetor. Obviously this can be effected in that both the crankcase and the carburetor axe equipped with an inlet nipple each, and these both nipples are connected by a hose. Such an arrangement is however relatively sensitive to damages at the same time as it is comparatively expensive. Therefore a solution has come up, where the inlet bellow proper is equipped with an extra duct for transferring said pressure pulses from the crankcase. This duct is lead beside the larger inlet duct. This solution will result in two disadvantages. Firstly, the arrangement with a small extra duct will result in a high cost for the bellow, and secondly this extra duct, which is associated with the larger inlet duct, will result in an essential stiffening of the entire inlet bellow. This is not desirable since vibrations are then easier transferred from the engine's cylinder onto the carburetor.
A similar design is used for the bellow of the chain saw model Stihl 017. However its carburetor is fixedly mounted to the power unit. There is therefore no anti-vibration suspension for the carburetor itself. Its inlet bellow also has an extra duct connected to the inlet duct in its entire length. This also results in an expensive and very stiff inlet bellow. The stiffness of the bellow is even used to accomplish, or contribute to, the sealing function at the area where the extra duct meets the cylinder. The extra duct of the inlet bellow ends up in a nose part with a conical exterior that is pushed into an aperture with a corresponding conical shape. When the carburetor is bolted to a part, to which also the cylinder is fixed, the conical nose part and the extra channel will be squeezed into the conical aperture to accomplish a sealing function.
The inlet bellow has a first flange part which has a projecting outer edge that is pushed upon a projecting inlet stud of the cylinder. A ring is pushed over the outer edge to accomplish sealing against the inlet stud. The inlet stud has no grooves or similar to create an axial fixation of the bellow. This fixation instead seems to be accomplished in that the carburetor pushes the very stiff bellow against the inlet stud. The very stiff bellow would be completely unsuitable for an anti-vibration suspension for the carburetor itself. And such a suspension is also not used in this chain saw model.